Unit 1.2.1: Exchange Surfaces and Breathing

The Lungs

The plasma membranes surrounding the thin cytoplasm of cells form a barrier permeable to oxygen and carbon dioxide.

The lungs produce a surfactant which reduces the cohesive forces between the water molecules. (Without it the alveolus would collapse as it would be unable to expand).

The Alveoli

Provides a large surface area for gaseous exchange.

Both the alveolus and the capillary wall is one cell thick and consists of squamous cells.

The capillaries are in close contact with the alveolus walls and are so narrow that the RBC's are squeezed against the capillary wall, reducing the rate at which they flow and making them closer to the air in the alveoli.

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Maintaining the Diffusion Gradient

Maintaining the Diffusion Gradient

Arich blood capillarynetwork ensures that there's always a high concentration of carbon dioxide and a low concentration of oxygen as the oxygenated blood is moved out of the lungs via the pulmonary veins.

Ventilationensures that there is always a high concentration of oxygen and a low concentration of carbon dioxide in the alveoli sacs to maintain the diffusion gradient.

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The Trachea And Bronchi

The trachea and bronchi have a similar structure and only differ only in size:

Much of the wall consists of cartilage; wich is in the form of C-rings.